1. Field of the Invention
The present invention relates to a road information providing device and a road information providing system with which, by data transfer being performed via communication between devices that hold different map data, for example between a terminal device and a server device of a navigation system, it is possible for the terminal device to utilize the most up-to-date information available upon the server device.
2. Description of Related Art
Navigation devices are per se well known and widespread that receive the most up-to-date information from an external communication center via a broadcast or via a communication device, and that obtain a route to a destination while taking into account this most up-to-date information. For example, as one of its basic functions, a navigation device may be provided with the function of receiving the newest traffic information, such as information about congestion or about traveling times or the like, in the form of an FM multiplex broadcast or the like provided from a traffic information center, and with a route guidance function of calculating the shortest time route to a destination using this traffic information. Moreover recently, in order to be able to forecast the time point of arrival at the destination more quickly and with better accuracy, and in order thus to arrive at the destination more efficiently, it has also been per se arranged for a navigation device to acquire from an information center predicted traffic information at the time point that it is predicted that the vehicle will pass, and for the navigation device, using this, to calculate and guide a route to the destination for which the time required will be a minimum. Moreover, there is also a per se known type of navigation system in which it is arranged for an optimum route calculated by an information center and reflecting the newest traffic information to be transferred to a navigation device, that then guides the vehicle along this optimum route to the destination.
This process need not be limited to traffic information; there is a movement to enrich navigation services by downloading to the terminal voluminous and moreover up-to-date information held on an external site. For example, property information such as route information to the destination, a recommended time for departure, possible locations for taking breaks, and so on may be provided at the user's home by a portal that supports journey planning, in consideration of the most up-to-date information such as ongoing changes related to facilities, charges for the use of roads, the level of usage of facilities, event information, and so on. A service also exists with which it is also possible, in order to guide the vehicle along a recommended route to its destination, to take advantage of information about a journey that has been planned upon a portal site, and that has been transferred to the navigation device via a removable medium or by electronic communication.
For road information that includes traffic information and/or route information to be used in common by both the center and by the navigation device, it is necessary for common position information to be handled by both devices. However, the navigation device is not necessarily limited to using the same type of map data (i.e. the same format for expressing positions) as the center. Moreover, even they both use the same type of map data, if their versions of the map data are different, then it is not necessarily the case that they will be able to use the same representation numbers (i.e., road link numbers) in common for road shapes and/or road positions.
Thus, with the VICS (Vehicle Information and Communication System) system, traffic information is provided by allocating unique numbers (VICS link numbers) to road sections (road links) for specifying roads that correspond to traffic information. In the navigation device, it is specified to which road the information that has been received corresponds, by using a correspondence table between road links of the map data maintained in the navigation device and VICS link numbers.
However, such VICS link numbers may not correspond to all of the roads of the map data held by the navigation device. Thus, since traffic information is not provided for roads for which VICS link numbers are not defined, accordingly there is a possibility of encountering congestion that has not been predicted on this type of road for which no VICS link number is as yet defined, and this entails a possibility of great variation from the forecast traveling time to the destination.
As a method for specifying the positions of a road to which no VICS link number is allocated, there is the method of using a coordinates-of-position string based upon latitudes and longitudes.
For example, in Japanese Laid-Open Patent Publication 2001-41757, there is disclosed a method of using a coordinates-of-position string as a method of position specification between maps that differ, in which a terminal device specifies a road section by determining its road shape from a coordinates-of-position string that is sent from a center, and by performing shape matching processing to search for a section over which the road shape that has been determined and the road shape of the map in the terminal agree with one another.
Furthermore, in Japanese Laid-Open Patent Publication 2003-121170, there is disclosed a method in which a center specifies and transmits road information to be provided, and/or a road link that specifies locations correlated with that road information, as a coordinates-of-position string that includes the start and end points of that road link, and in which the terminal device that receives this coordinates-of-position string specifies the road link that it describes as a road link on a terminal map, by using the coordinate values of that coordinates-of-position string sent from the center and the length and/or the azimuth of the line that joins its start and end points, and so on.